Worst case scenario, you get to MK before it opens, you go to one of the castmembers mulling around the entrance kiosks or go to the ticket booth and someone there will tell you what to do.
You probably will get there and Main street will be open, then go down the street until just before the bridge (there should be a rope or some time of divider across the road) at that point CP is on your left, simply tell one of the CMs you have a breakfast ressie @ CP and they will either just let you go or have walkie talkies and can check your name to your ressie. Don't worry about it, they do it allthe time, you will get in. Have fun!
LL